dynamic-link issue: does not always load

[Matt Wette <matt.wette@gmail.com>]

There is an old bug report #21076 on dynamic-link:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21076

Say you have a file libyaml.0.so-2, dynamic-link can't load it

     (dynamic-link "libyaml.0.so-2") => exception

even if there is a file libyaml.so:

   $ cat /usr/lib64/libyaml.so
   INPUT(libyaml-0.so.2)

it fails with (dynamic-link "libyaml")

I have submitted the following patch, which at least
makes the first version work.  If you think this is a libtool
but you may be right, but the bug report on this has not
been touched for 8 years:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=8976

This patch fixes issue with libtool and OSes which use
non-standard extensions for shared libraries.  The libltdl
function lt_dlopenext expects the argument to have a standard
extension or no extention.  Arguments reflecting shared object
files with non-standard extensions will fail to load.  For
example, my system has /usr/lib64/libyaml-0.so.2.  w/o this
patch (dynamic-link "libyaml-0.so.2") does not work; with it,
it does.  Go figure.

--- libguile/dynl.c-orig    2020-03-20 05:56:42.101214929 -0700
+++ libguile/dynl.c    2020-03-20 05:57:40.432893330 -0700
@@ -69,7 +69,10 @@
      handle = lt_dlopen (NULL);
    else
      {
-      handle = lt_dlopenext (fname);
+      handle = lt_dlopen (fname);
+
+      if (handle == NULL)
+         handle = lt_dlopenext (fname);

        if (handle == NULL
  #ifdef LT_DIRSEP_CHAR